Bug Wars: Heavy rains are good news, bad news in mosquito battle

Friday

Aug 19, 2011 at 12:01 AMAug 19, 2011 at 7:04 PM

Recent rains have cleared drains of some larvae, but mosquito foes are warning that saturated wetlands and containers that trap water could still breed bugs capable of spreading the West Nile and Eastern equine encephalitis viruses.

Michael Morton/Daily News staff

Recent rains have cleared drains of some larvae, but mosquito foes are warning that saturated wetlands and containers that trap water could still breed bugs capable of spreading the West Nile and Eastern equine encephalitis viruses.

"I would not sit out after dusk without repellent on," said Superintendent David Henley of the East Middlesex Mosquito Control Project, whose members include several MetroWest towns. "And it's a good time to check your yard for any kind of water."

Already, West Nile-infected mosquitoes have turned up recently in traps on Foley Drive in Natick and North Quinsigamond Avenue in Shrewsbury.

In other towns, health boards have been left to watch and wait, carrying on normal prevention efforts and ready to call for more spraying and educational campaigns if needed.

"It's business as usual," said Milford Health Director Paul Mazzuchelli, a commissioner for the Central Massachusetts Mosquito Control Project. "So far, so good."

While the state has not recorded a human West Nile case yet this year, seven people got sick last year. Most people don't fall ill if infected, but one-fifth experience symptoms like fever, fatigue and body-ache, usually lasting a few days. A tiny fraction gets hit harder, with people over 50 more susceptible.

In Natick, staff with the mosquito project treated catch basins with larvicide Wednesday and had plans last night to spray north of Bacon Street.

Shrewsbury has also asked them to treat drains near its positive test results.

"We use this as an opportunity to remind the public there are a number of steps they can take," Shrewsbury Health Director Derek Brindisi said.

Those steps include repairing screens; using repellant; wearing long sleeves, pants and socks; and avoiding peak feeding times, usually from dusk to dawn.

Residents are also asked to drain or discard items that might collect standing water, such as old tires, empty flowerpots or wading pools.

While the West Nile samples likely came from mosquitoes hatched before the rains, control agencies project that the downpours will influence disease spread. The storms flushed fresh water through fetid catch basins where the virus-carrying species likes to lay eggs, but also filled containers.

"Overall, there's a lot more water out there," Henley said, with West Nile typically a risk up to early October.

The East Middlesex head has tromped around the region gauging the rains' impact, visiting the Concord River yesterday and planning to hit the Sudbury River today. He's found that swamps and floodplains have quickly dried up for the most part, but that some riverbank sections, such as those in Wayland and Sudbury, are ripe for mosquito hatchings next week.

"I'm just not sure how much of an increase," he said.

Different species of mosquitoes are potential hosts to different viruses, and wetlands like those on the banks of the Sudbury are attractive to the kinds that can carry Eastern equine encephalitis, or EEE.

Like West Nile, there have been no human cases of EEE this season in the state, though it struck one resident and a visitor from Rhode Island last year. Roughly 5 percent of infected people develop symptoms, with chills, fever and malaise; one-third of those people die.

So far, state EEE samples have been confined to Plymouth and Bristol counties.

"It's something you need to worry about with these new mosquitoes," said John Smith of the Norfolk County Mosquito Control Project, whose members include Bellingham, Franklin and Medway.

(Michael Morton can be reached at 508-626-4338 or mmorton@wickedlocal.com.)